|I have black bugs (small and round) on the underside of my papayas. The damage is most severe on the oldest leaves (lighter in color than than they should be and exhibit a light marbled discoloration) which turn yellow and shrivel up and die. My Daturas have a similar affliction but the pest is tan and larger than the Papaya pests.|
|It sounds like you have scale, most likely one of the tortoise scales. Summer or horticultural oil (not dormant oil) is an option for scale control. Try it first on a section of the plant to make sure it is not going to "burn" the foliage. Even these lighter weight oils can be a problem for some plants in the summer. The oil must be sprayed upward to contact the pest or they will not be effective.
I would also suggest you take a sample of the pests into a knowledgeable nursery professional or your county Extension office. With the actual culprit in hand they should be able to give you an accurate identification and perhaps suggest other appropriate options for control.